This invention relates to ignition devices in particular to those capable of discharging sparks from ignition plugs substantially continuously over a long period of time. A conventional ignition device used in spark-ignition engines comprises an ignition coil and a breaker for causing, for every combustion cycle of an engine, single or multiple instantaneous discharges from the ignition plugs to ignite a compressed gaseous mixture.
However, such conventional devices cannot provide satisfactory ignition performance when the gaseous mixture is lean or a large amount of exhaust gas recirculation is effected, thus resulting in lower fuel economy and production of a great amount of harmful components in exhaust gases.